1. Field of the Invention
The present invention relates to a reinforced polypropylene resin composition suitable particularly for instrument panels. More particularly, the present invention is concerned with a reinforced polypropylene resin composition having a good moldability and such well balanced properties that when it is molded into an article, the molded article has a tensile strength, a flexural modulus, a flexural strength, a hardness, a falling ball impact strength and other properties sufficient for practical use and is excellent in other properties and less susceptible to warpage deformation while maintaining the rigidity and impact resistance at a high temperature.
2. Description of the Prior Art
In order to improve the mechanical strength, rigidity, heat deformation resistance and other properties, it is a common practice to incorporate into polypropylene various fillers, for example, fibrous fillers such as glass fibers, carbon fibers, whiskers or metallic fibers, flaky fillers such as mica, talc, kaolinite or glass flake, and particulate fillers such as calcium carbonate, diatomaceous earth, alumina or glass beads. This method has already found wide applications.
Among the above-described fillers in various forms, the fibrous fillers exhibit a much better reinforcing effect than do the fillers in the other forms. Especially, a polypropylene resin composition reinforced with a glass fiber has found wide use in various fields as a material suitable for the production of a molded article having high rigidity and high heat resistance.
However, when the glass-fiber reinforced polypropylene resin composition is molded into particularly a large-sized article, the product is free from the problem in respect of the rigidity and heat resistance, but is liable to exhibit a larger "warpage" (deformation). This is a problem encountered when the glass-fiber reinforced polypropylene resin composition is used as a molding material for a large-sized molded article.
On the other hand, the use of a flaky filler and a particulate filler as a filler for the polypropylene resin reduces the warpage deformation. In this case, however, the effect of reinforcing the tensile strength, flexural modulus, flexural strength, Izod impact resistance and thermal rigidity is much smaller than that in the case where use is made of a fibrous filler. Nevertheless, since a molded article of a polypropylene resin composition reinforced with a flaky filler, such as mica or talc, exhibits a good rigidity, an attempt has been made on the combined use of a fibrous filler and a flaky filler. This is disclosed in, for example, Japanese Patent Laid-Open Nos. 36141/1977, 130647/1979, 16049/1980, 21438/1980, 45715/1980, 206659/1983, 226041/1984, 23432/1985 and 98758/1986.
Even the inventions disclosed in the above-described documents, however, cannot provide any molded article satisfying requirements for warpage and torsion.